Estimating tidal current amplitudes outside estuaries and characterizing the zone of estuarine tidal influence

Theoretical predictions are consistent with observed tidal current amplitudes outside the Delaware Bay and Block Island Sound. In both test cases, the estimated and observed amplitudes exhibit an r−2 dependence and decay over a similar distance. The relative importance of estuarine tidal influence is assessed with the tidal interaction index (Ti=ue/ua). The intensity of estuarine influence is characterized by the value of Ti at the mouth (Tim). The extent of an estuary-shelf tidal interaction zone is measured by the interaction radius ri (where Ti=1) and by r∞ (where Ti=0.1). These metrics are used to compare the tidal interaction zone characteristics for the Delaware Bay, Block Island Sound, several other major estuaries, and a small tidal inlet. The kinematic theory can be applied outside other estuaries where only limited tidal information is available or used to interpret observed patterns in tidal amplitudes and characterize the degree of estuarine influence.